Males and females look and behave very differently and are rarely seen by people. Mature strepsipterans are 3 mm (0.13 in) long. Males are free-living; their front wings are small and clublike, while their rear wings are broad and membranous, with few veins. They have protruding eyes and prominent branched antennae. When mature, males exit their host and search for females. They are guided by volatile odors, or pheromones to host insects parasitized by females of their species. Only the female's head protrudes from the host's body; the male mates by inserting sperm into the neck region of the female.
Females of most species never leave their host. In general, they are wingless and grublike, lacking eyes, antennae, and appendages. Their head and thorax are fused, and their somewhat swollen abdomen has indistinct segments. After mating, each female produces many tiny young, sometimes several thousand. The hatchling larvae are known as triungulins; they are active, host-searching parasites with well-developed eyes and legs. After emerging from their mother's body and that of her host, they drop to the soil or vegetation and begin to search for hosts of their own. They often wait on flowers for wasps or bees, and some may be ingested by the host as it sucks up nectar. Others use enzymes to digest their way through the host's cuticle.
Both sexes undergo hypermetamorphosis: radical changes in body form with each growth stage. Once inside a host, the triungulin molts into a legless larva and feeds inside on the host's blood. After about four molts, the larva pupates inside the host. If it is a male, it emerges and flies to seek females. If it is a female, it waits to mate and produces young and then dies within its host. Strepsipterans do not always kill their hosts, but may sterilize them or cause deformities in shape or color. Insects that have been parasitized in this way are said to by "stylopized," after the most common genus of strepsipterans.
Strepsipterans share many characteristics with two families of parasitic beetles, and are considered by some experts to be beetles themselves. They are notoriously difficult to study because they are so hard to find. Males are sometimes collected by entomologists along with other insects; the females of many species have never been described. Undoubtedly, many species remain to be discovered.
Scientific classification: Strepsipterans comprise the order Strepsiptera, from the Latin strepsi (twisted) and ptera (wings). The largest genus is Stylops, in the family Stylopidae. Strepsipterans are closely related to beetles and some taxonomists classify the family stylopidae in the order Coleoptera.